The overriding goal of the proposed project is to better understand the diagnostic entity of posttraumatic stress disorder (PTSD) and its causal antecedents. Using existing data from the National Veterans Readjustment Study, this global goal will be achieved through the accomplishment of five specific aims: Specific Aim 1: To provide empirical support for subtypes of PTSD> Cluster analysis first will be used to identify groups of PTSD-positive veterans sharing common symptom patterns, and multi-sample confirmatory factor analysis will document the nature of group differences. Confirmatory factor analysis will also be used to examine the comorbidity of the resulting PTSD subtypes with other diagnoses. Specific Aim 2: To validate multiple dimensions of wartime trauma and their relationships to PTSD and other adjustment outcomes. A rational approach to instrumentation and item response theory technologies will be used to develop reliable measures of trauma. These measures then will be submitted to confirmatory factor analysis and correlated with adjustment outcomes to establish discriminant and criterion-related validity. Specific Aim 3: To evaluate the causal influences of premilitary disposition variables on PTSD. A two-step structural equation modeling approach, incorporating measurement and structural components, will evaluate the direct influences of premilitary factors on PTSD, their indirect influences on PTSD, an the extent to which they interact with level of wartime trauma to influence PTSD. Specific Aim 4: To assess the mechanisms whereby postwar social support and postwar stressful life events impact PTSD. Again, two-step structural equation modeling approach will be used to assess both the direct effects of these postwar variables on PTSD and the extent to which they interact with trauma to influence PTSD. Specific Aim 5: To test an integrated model of the network of causes of PTSD. The project will culminate with a double cross-validation structural equation modeling strategy to examine PTSD etiology as a function of premilitary, trauma, and postwar factors.